A vehicle typically includes a climate control system which maintains a temperature within a passenger compartment of the vehicle at a comfortable level by providing heating, cooling, and ventilation. Comfort is maintained in the passenger compartment by an integrated mechanism referred to in the art as a heating, ventilation and air conditioning (HVAC) air-handling system. The air-handling system conditions air flowing therethrough and distributes the conditioned air throughout the passenger compartment.
The air-handling system commonly employs a housing having a plurality of passageways and doors for controlling a temperature and a flow of the air therethrough. The housing may for example be divided into an inlet section, a conditioning section, a mixing section, and a delivery section. The inlet section may include a blower or fan for delivering the air to the conditioning section. The conditioning section includes one or more heat exchangers for controlling a temperature and humidity of the air. Control features disposed within the conditioning section control the flow of the air through passageways having the heat exchangers disposed therein. For example, temperature doors, or otherwise referred to as flaps or valves, can be employed to control the flow of the air through passageways having the heat exchangers disposed therein. The mixing section is disposed downstream of the conditioning section and forms a chamber for recombining each of the streams of air, whether heated or cooled, exiting the conditioning section. The delivery section includes a plurality of conduits or ducts branching from the mixing section for delivering the air to the desired vents located within the passenger compartment of the vehicle.
The vents disposed within the passenger compartment may include panel vents, console vents, front floor vents, rear floor vents, windshield defrost vents, and side window defrost vents, for example. The delivery section is configured to deliver the air originating from the mixing section to any combination of the vents based on the operating mode selected by a passenger of the vehicle. Each operating mode includes a preselected percentage (or distribution ratio) of the air originating from the mixing section delivered to each of the corresponding vents associated with the selected operating mode. Doors disposed within the delivery section may be actuated to control the distribution of the air to each of the desired vents by blocking or opening various passageways disposed within the delivery section. For example, a “panel operating mode” may include the air distributed only to the panel vents and the console vents, a “defrost operating mode” may include the air distributed only to the windshield defrost vents and the side window defrost vents, and a “floor operating mode” may include the air distributed to each of the front floor vents, the rear floor vents, the windshield defrost vents, and the side window defrost vents.
One problem associated with the distribution of the air to each of the vents of the delivery section relates to differences in a volumetric flow rate and a pressure of the air required at the outlet of each of the vents to achieve the desired distribution of the air for each of the operating modes. Because each of the vents of the delivery section receive air from the mixing section wherein the air has a common pressure value, each portion of the delivery section fluidly coupling the mixing section to a corresponding vent must be constructed or otherwise controlled to cause a desired pressure drop in the air to meet the desired conditions at the outlet of each of the vents. One method of controlling the pressure drop is to variably restrict or open one or more flow paths through which the air passes for a given operating mode. The variable restriction or opening of the flow paths may be achieved by actuating one or more doors disposed within the flow paths to control the pressure and flow rate of the air through each of the flow paths.
The problem associated with the control of the flow of the air through each independent flow path is especially evident when attempting to control the pressure of the air associated with the outlets of the windshield defrost vents and the outlets of the side window defrost vents. It is common for the flow path leading to the windshield defrost vents and the flow path leading to the side window defrost vents to branch from a common portion of the delivery section due to these vents commonly being used together during various operating modes of the air handling system. For example, the flow path leading to the windshield defrost vents and the flow path leading to the side window defrost vents may each branch from a defrost chamber of the delivery section separated from the mixing section by an actuated door. Upon opening the door, air from the mixing section flows into the defrost chamber before branching to one or both of the windshield defrost vents and the side window defrost vents. In certain operating modes of the air handling system, a pressure required at the outlet of each of the windshield defrost vents to achieve a desired volumetric flow rate of the air through the windshield defrost vents may differ in comparison to a pressure required at the outlet of each of the side window defrost vents to achieve a desired volumetric flow rate of the air through each of the side window defrost vents. For example, when operating in the floor operating mode, the windshield defrost vents may require a duct pressure of about 5 PA to deliver the air out of the windshield defrost vents at a volumetric flow rate of about 30-40 m3/h whereas the side window defrost vents may require a duct pressure of about 175 PA to deliver the air out of the side window defrost vents at the same volumetric flow rate of about 30-40 m3/h. In contrast, when operating in the defrost operating mode, the windshield defrost vents and the side window defrost vents may each require approximately the same duct pressure of about 225 PA to deliver the air out of the windshield defrost vents and the side window defrost vents at their required volumetric flow rates of about 250-325 m3/h and 35-45 m3/h, respectively. The potential difference in pressure required at each of the respective vent outlets accordingly frustrates an attempt to control the pressure within each independent flow path by actuating the door disposed upstream of the defrost chamber as an attempt to control the pressure in one of the flow paths may adversely affect the ability to control the pressure in the other of the flow paths.
This problem is further evident in view of changing demands in the distribution of the air to the various vents of the passenger compartment based on the corresponding operating mode, and especially changing demands to the percentage of the air delivered to the side window defrost vents during the floor operating mode, the defrost operating mode, and a mixed floor/defrost operating mode. For example, in traditional air handling systems the floor operating mode may include about 75% of the air delivered to the floor vents, about 17% of the air delivered to the windshield defrost vents, and about 8% of the air delivered to the side window defrost vents. The traditional mixed floor/defrost operating mode may include about 56% of the air delivered to the floor vents, about 34% of the air delivered to the windshield defrost vents, and about 10% of the air delivered to the side window defrost vents. The traditional defrost operating mode may include none of the air delivered to the floor vents, about 80% of the air delivered to the windshield defrost vents, and about 20% of the air delivered to the side window defrost vents.
In contrast, newer air distribution requirements require the distribution of the air to the side window defrost vents to be elevated while also remaining substantially constant throughout the different operating modes utilizing the side window defrost vents. For example, the new requirements for air distribution during the floor operating mode may include about 72% of the air delivered to the floor vents, about 10% of the air delivered to the windshield defrost vents, and about 18% of the air delivered to the side window defrost vents. The new requirements for the mixed floor/defrost operating mode may include about 56% of the air delivered to the floor vents, about 30% of the air delivered to the windshield defrost vents, and about 14% of the air delivered to the side window defrost vents. The new requirements for the defrost operating mode may include none of the air delivered to the floor vents, about 80% of the air delivered to the windshield defrost vents, and about 20% of the air delivered to the side window defrost vents. Accordingly, in contrast to the traditional requirements wherein the percentage and/or airflow volume of the air distributed to the side window defrost vents more than doubled between the floor operating mode and the defrost mode, the new requirements include the percentage and/or air flow volume of the air distributed to the side window defrost vents remaining substantially constant throughout all three of the operating modes including a defrost function. This relationship presents a situation wherein the pressure at the outlets of the side window defrost vents must remain substantially constant for all three operating modes whereas the pressure at the outlets of the windshield defrost vents must vary significantly depending on the selected operating mode.
One solution to the differing pressure requirements between the windshield defrost vents and the side window defrost vents is to provide a separate door for controlling entry into each flow path branching from the defrost chamber. However, this solution may require the addition of multiple components such as doors, actuators, links, or control elements, thereby increasing a cost and complexity to manufacture the air handling system.
The change of the distribution of the air to the windshield defrost vents and the side window defrost vents also poses additional problems relating to the noise, vibration, and harshness (NVH) generated by the flow of the air while flowing through the delivery section. The windshield defrost vents and the side window defrost vents may typically require a relatively small percentage of the air from the mixing section distributed thereto for various operating modes. These conditions may result in a situation where the air delivered to either of the windshield defrost vents or the side window defrost vents must travel through a relatively small and relatively uncontrolled gap while passing from a high pressure chamber (the mixing section) to a relatively low pressure chamber (the defrost chamber of the delivery section), thereby resulting in a rapid expansion of the air in a manner that may cause unwanted NVH.
A control and minimization of NVH is particularly desired in the floor operating mode. In the floor operating mode, air is delivered to the windshield defrost vents in a bleed condition through the relatively small gaps, as mentioned hereinabove. In the prior art, the relatively small gaps are fixed orifices in or adjacent to the door allowing the air to travel therethrough to the windshield defrost vents. However, the problem with the orifices is there is no way to close or completely seal the defrost chamber in the delivery section from the air flowing from the mixing section without additional components such as an extra door, for example. Another known solution has been to open the door in the defrost chamber minimally in order to achieve the relatively small gap. However, the problem with this solution is distribution of the air flowing through the defrost chamber is difficult to control and generates increased undesired NVH. With the newer air distribution requirements, especially when the floor operating mode is selected, it is especially desired to manage air flow through the delivery section to achieve desired resistance control along the path of the air distributed to the windshield defrost vents while minimizing resistance along the flow path of the air distributed to the side window defrost vents.
Accordingly, there exists a need in the art to efficiently and cost effectively control a distribution of air to the windshield defrost vents and the side window defrost vents of an air handling system while preventing an incidence of noise, vibration, and harshness.